Sarah Palin, the former Alaska governor and 2008 vice-presidential nominee who became a Tea Party sensation and a favorite of grass-roots conservatives, will endorse Donald J. Trump in Iowa on Tuesday, officials with his campaign confirmed. The endorsement provides Mr. Trump with a potentially significant boost just 13 days before the state’s caucuses.

“I’m proud to endorse Donald J. Trump for president,” Ms. Palin said in a statement provided by his campaign.

Her support is the highest-profile backing for a Republican contender so far.

“I am greatly honored to receive Sarah’s endorsement,” Mr. Trump said in a statement trumpeting Mrs. Palin’s decision. “She is a friend, and a high-quality person whom I have great respect for. I am proud to have her support.”

In Iowa, where Ms. Palin spent years developing support, the endorsement could be especially helpful.